The inventive concept relates generally to semiconductor memory devices and nonvolatile memory devices in particular.
Semiconductor memory devices may be broadly classified as volatile or non-volatile in their operative nature. Volatile memory devices lose stored data in the absence of applied power, and include Static RAM (SRAM), Dynamic RAM (DRAM), Synchronous DRAM (SDRAM), and the like. Non-volatile memory devices retain stored data even in the absence of applied power. Non-volatile memory devices include Read Only Memory (ROM), Electrically Programmable ROM (EPROM), Electrically Erasable and Programmable ROM (EEPROM), flash memory, Phase-change RAM (PRAM), Magnetic RAM (MRAM), Resistive RAM (RRAM), Ferroelectric RAM (FRAM), and the like. Flash memory is currently an important type of non-volatile memory and includes NOR-type flash memory and NAND-type flash memory.
Increasing demand for data storage density per unit area occupied by semiconductor memory devices has motivated the development of semiconductor memory device having three-dimensional (3D) memory cell array architectures. However, the effective design and fabrication of 3D memory cell arrays are difficult tasks.